In manufacturing electronic devices such as semiconductor devices, a plasma processing apparatus is used for processes such as etching and film formation. A capacitively coupled plasma processing apparatus is known as one type of plasma processing apparatus. The capacitively coupled plasma processing apparatus generally includes a chamber body, an upper electrode, and a lower electrode. The upper electrode and the lower electrode are disposed such that an internal space of a chamber provided by the chamber body is defined between the upper electrode and the lower electrode. In this plasma processing apparatus, a gas is supplied to the chamber and a high frequency electric field is formed between the upper electrode and the lower electrode. The gas is excited by the high frequency electric field to generate plasma. A workpiece is processed by the ions and/or radicals produced from the plasma.
Further, a plasma processing apparatus configured to distribute a high frequency from a single high frequency power supply to an upper electrode and a lower electrode is known as one type of capacitively coupled plasma processing apparatus. This plasma processing apparatus includes a transformer. The transformer is provided with a primary coil and a secondary coil. The primary coil is connected to the high frequency power supply. One end of the secondary coil is connected to the upper electrode, and the other end thereof is connected to the lower electrode. The secondary coil has a plurality of taps selectively connected to a ground. In this plasma processing apparatus, a ratio of the electric power of the high frequency supplied to the upper electrode and the electric power of the high frequency supplied to the lower electrode, i.e., an electric power ratio, is adjusted by changing the respective tap to be connected to the ground. Such adjustment of the electric power ratio adjusts the energy of the ions incident to a workpiece disposed on the lower electrode.
In addition, a plasma processing apparatus including a filter having variable impedance installed between a lower electrode and a ground is known as another type of capacitively coupled plasma processing apparatus. In this plasma processing apparatus, a current flowing into the lower electrode is adjusted by adjusting the impedance of the filter. Such adjustment of the current adjusts the energy of the ions incident to a workpiece disposed on the lower electrode.
In the plasma processing apparatus, it is required to process a workpiece by the ions of various kinds of energies. Thus, in the capacitively coupled plasma processing apparatus, the adjustable range of the energy of the ions incident to a workpiece disposed on an electrode is required to be enlarged.